The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
GDI has begun to be developed with a rise in demand for developing a high-pressure injector and improving fuel efficiency. A GDI engine can remarkably improve fuel efficiency through a combustion system that can perform ultra-lean combustion of about 40:1 during a part load operation.
A GDI engine, as shown in FIG. 1, includes an intake port 12 for guiding intake air with a strong tumble into a combustion chamber 11 and an exhaust port 13 for exhausting combustion gas, wherein an injector 14 that directly injects fuel into the combustion chamber 11 is disposed at a side from the intake port 12 and a spark plug 11 that ignites the fuel injected from the injector 14 by producing a spark is disposed over the combustion chamber 11. In particular, a bowl 17 for enhancing flow of intake air is formed on the top of a piston 16.
Accordingly, intake air flowing into the bowl 17 through the intake port 12 is enhanced in flow while flowing on the wall of the bowl 17, and the fuel directly injected from the injector 14 hits the wall of the bowl 17 whereby it evaporates on a hot surface of the piston 16 and is mixed with the intake air upon evaporating due to the strong flow of the intake air in the bowl 17, thereby producing a stratified gas mixture. Although the gas mixture is in an ultra-lean state in the entire combustion chamber, a stratified condensed gas mixture is produced around the spark plug, and combustion occurs in this state.
As described above, the flow of the intake air is enhanced when the intake air hits the wall of the bowl 17 formed on the top of the piston 16 and the fuel injected from the injector 14 also hits the wall of the bowl 17. This area of the bowl 17 that the fuel hits is called a wall guide bowl.
We have discovered that since the fuel injected into the bowl evaporates while hitting the wall of the piston, it evaporates later than the fuel that does not hit the wall of the piston. Accordingly, the fuel that evaporates late takes part in combustion later, so it produces soot and increases hydrocarbon (HC) exhaust.
In particular, we have found that in cold start condition (e.g., when the piston is not heated), a larger amount of smoke is exhausted and the flow of the intake air is enhanced only through the intake port, so performance under full load is decreased by load on the intake port.
The foregoing is intended merely to aid the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.